Hi Tom,
The Sand Pebbles was our first T+T convention game. We modified the story a little, but the game was based on the movie. It was a multi player ( 4 gamers ) game. Contact me for more info if you like. Our gun boat was stationary at the pier so we didnt design special rules for gun boats. T+T has rules for lmg, hmg, guns, mortars etc. I think you can easily develop some rules for gun boat movement ramming, damage etc.
Cheers
Björn